Stanford researcher Yi Cui looked across the field of transparent
electronics and saw that all was not equal. While all other major
electronics components--things like transistors, displays, and other
circuitry--have been made transparent, no one had taken the time and
effort to create a transparent power source. And you can’t have a fully
transparent device without a transparent battery. So Cui made one.

There are a few ways to make an electronic component transparent. One
is to make it so thin that it doesn’t register with the human eye. Or
you can make the component take the form of a pattern whose features are
so small they are invisible. Some battery components are easy to render
transparent by shrinking them, but electrodes are particularly
difficult to make thin. A super-thin electrode isn’t energy dense, and
therefore it doesn’t store up enough power to be useful in any realistic
way.

So
Cui opted for the second approach. He and his team figured that if you
can pattern the electrode into a superfine mesh, you can still build an
energy dense battery. With enough electrode material distributed across
the mesh, a battery can still hold a significant charge.